In wireless communications systems applying Long Term Evolution (LTE) protocols and standards, the mobile unit, or User Equipment (UE) operates on one of two states relative to the radio interface maintained with a serving base station, or enhanced Node B (eNB). Those states are designated RRC_Connected and RRC_idle (RRC indicating “Radio Resource Control”). In the RRC_Connected state, the UE maintains an active connection with the eNB, while in the RRC_idle state, no connection exists between the UE and the eNB, with the UE waking up (turning on its receiver) at defined intervals to listen for pages from an eNB. As will be apparent, battery resources in the UE and RF resources in the cell in which the UE is operating will be much more heavily consumed in the RRC_Connected state than in the RRC_idle state (and, as well, intra-cell and inter-cell interference associated with the maintenance of an active connection between the UE and eNB will be largely absent in the RRC_idle state).
As implied in the prior paragraph, in the current LTE framework, a UE can only send user data to the wireless network (via its serving eNB) when the UE is in the RRC_Connected state. For a large data communication transaction, that is not an issue. However, for very small data transactions—e.g., a text message sent via the Short Message Service, setup for the connection encompasses substantial overhead in both connection maintenance and signaling, often consuming more system resources than that needed for the data transmission. This problem will certainly be exacerbated as the evolving field of Machine-to-Machine (M-to-M) communications via wireless connections continues to gain traction. With Machine-to Machine communications, the individual data transaction will in most cases be quite small, while the population of M-to-M transmitters is potentially very large—producing a load on the wireless system of a very large number of quite short data transactions.
Under the LTE standard, the eNB needs to either setup an RRC connection for each of the small transactions, and then tear-down the connection as soon as the data transaction is completed, or maintain a large number of idle RRC connections. Neither option permits an efficient utilization of wireless system resources.
To some degree, the signaling overhead associated with RRC connection is mitigated through operation of a procedure known as MAC-DRX, which allows the UE to periodically go to sleep if there is no traffic activity, while remaining in the connected state. However, while MAC-DRX effects a saving in UE battery consumption, it does not reduce eNB processing because eNB still needs to maintain the UE's RRC connection. In addition, this increases dramatically the handover activities because the UE is always in the RRC_Connected state, so mobility management effort is magnified.
With the increasing popularity of thin-traffic applications, the LTE infrastructure faces huge pressure to support a large number of RRC connections per cell in DRX mode, which becomes very challenging for the entire eNB population and the evolved packet core. Meanwhile user performance is less than optimal as well. For example, if the eNB needs to send data to a UE during the DRX OFF period, the eNB has to wait until UE comes out of DRX OFF and becomes active, which also incurs nontrivial delay.